The present invention relates to a device for cooling the battery or batteries of notably an electric motor vehicle, of the hybrid or all-electric type.
Vehicles with an electric motor are fed with electric power by a battery the life of which is crucial considering its initial price.
These electrochemical batteries, very sensitive to temperature variations, are usually designed to operate optimally in a temperature range of 20 to 40° C., or even of 20 to 30° C.
A temperature higher than 40° C. makes it possible to improve the performance of a lithium battery but increases its speed of deterioration, a temperature of 40° C. already being high for ensuring a long life.
A temperature higher than 40° C. for a battery of the NiMH (or NiCd) type affects the charging capacity of the battery and accelerates its rise in temperature.
Because of their relatively large size and weight (typically 15 to 20 kWh for a battery of 150 to 200 kg providing a range of 100 to 150 km), these batteries increase in temperature slowly but are difficult to cool.
Since the generation of heat is proportional to the square of the electric current and the power is proportional to the current, the generation of heat is proportional to the square of the power.
A very rapid charge of the battery (in approximately fifteen minutes) can therefore cause a generation of very great heat in the battery.
In the case of a system for rapidly charging the battery, the driver may use the vehicle several times in the same day by rapidly charging the battery after it has been completely discharged following the use of the vehicle.
In this case, the temperature of the battery will increase more and more until it reaches the maximum authorized temperature, the battery not having the time to cool between two rapid charging cycles of the battery.
It is then necessary to cool the battery in order to protect its life.
The document U.S. Pat. No. 5,834,132 proposes a system for regulating the temperature of a battery of a motor vehicle.
This system proposes a cooling circuit traveling between the cells of the battery, this circuit being supplied with cooling fluid by a reservoir.
A pump is necessary for circulating the cooling fluid.
The fluid is cooled by the outside air by means of a radiator and an associated fan.
However, in order to ensure an effective cooling, the dimensions of the radiator and the capacity of the fan must be considerable, the temperature differences between the outside air and the fluid and between the battery and the fluid being relatively small.
The result of this is a relatively large bulk and weight of such a system, which moreover is complex and costly because of the cooling circuit, the pump, the radiator and the ventilator, which are large in size, and because of the necessary valves.
Moreover, such a system is not sufficiently effective to cool the battery in the case of successive rapid charges because of the generation of very considerable heat in a very short time.
Another known cooling device uses the air-conditioning system of the vehicle to cool the battery or batteries.
This device is fitted to the vehicles of the Ford Escape type and is shown diagrammatically in FIG. 1.
This device comprises an evaporator 1 situated in the passenger compartment 2 which is connected to the condenser 3 situated outside the passenger compartment by two ducts 4, 5 in which a coolant, such as Freon, that is compressed in a compressor 6, flows.
The two ducts 4, 5 are connected to two branch ducts 7, 8 that are connected to an evaporator 9 which cools the inside of a casing 10 enclosing the batteries 11.
The holders 12, 13 make it possible to regulate the flow of the coolant in the ducts 4, 5 and 7, 8.
The drawback of this cooling device lies in the fact that the evaporator 9 is situated in the casing 10 which encloses the batteries, which increases the volume of this casing 10 and complicates the connection between the evaporator 9 and the branch circuit of the coolant, which poses problems when it is desired to remove the casing 10 from the vehicle.